Segment for a core drill bit and method of manufacture

ABSTRACT

A core drill bit segment ( 10 ) comprises an elongated member ( 12 ) having an upper end ( 14 ), a lower end ( 16 ), first side ( 18 ) and opposite second side ( 20 ). Attached to the lower end ( 16 ) is matrix ( 22 ). The matrix ( 22 ), while depending from the lower end ( 16 ) also extends upwardly toward the upper end ( 14 ) along first and second sides ( 18, 20 ) of the member ( 12 ). The lower end ( 16 ) is provided with a lip ( 24 ) that is turned upwardly to extend in front of the first side ( 18 ) to define a recess ( 26 ) for seating a lower edge of a drive sub ( 25 ).

FIELD OF THE INVENTION

[0001] The present invention relates to a segment for a core drill bit and to a method of manufacture of the segment.

BACKGROUND OF THE INVENTION

[0002] The present Applicant is the proprietor of the RETRACTABIT retractable drill bit system. This system is the subject of numerous patents including U.S. Pat. Nos. 5,662,182; 5,954,146; 5,813,481; 5,743,344 and 5,785,133. The system incorporates a core drill bit composed of a plurality of separate segments that can be replaced in situ without the need to pull an associated drill string.

[0003] Each bit segment is in the form of an elongated member having an upper end configured to engage a seat in a drive sub, opposite first and second sides which are configured to cooperate with adjacent surfaces of the drive sub and a bit locking sleeve, and a lower end to which is fixed a matrix. The matrix is of conventional form comprising a combination of metal powders and diamonds which are bonded to the lower end of the members by application of heat and pressure.

[0004] Due to the structure of the RETRACTABIT drill bit the area of matrix is reduced to about 60% of a standard wire line core bit of the same diameter. Therefore, in order to achieve the same penetration rates as with a standard wire line core less weight is required on the RETRACTABIT drill bit. Nevertheless, in practice it has been found that at times drill rig operators apply the bit weight for standard wire line core bits which, for an NQ size bit is in the order of 1350-2000 kg and, for a HQ size bit is between 1800-3600 kg. The ideal weight applied to the corresponding sized RETRACTABIT drill bits is 810-1680 kg; and 1080-2160 kg respectively.

[0005] It is thought that if the applied weight is the same as a standard wire line core bit, over penetration will occur resulting in inner diameter gauge and concave face wear. This arises because a lower end of the segments bend or pivot in an uncontrolled manner toward or away from an axis of the hole being drilled. This produces variations in the diameter of the core being cut. A reduction of the outer diameter of the core can result in a core catcher held within the drill being unable to grip the core, which is a requirement in order to allow core breaking to occur or alternately the core catcher holding the core with insufficient force so that the core slips out of a core tube while being pulled to the surface. If the diameter of the core being cut is oversized it forces the core tube in the upward direction inside the drill string shutting a fluid valve in the drill string causing an overpressure condition resulting in a shut down of the drill.

[0006] Further to the above, as the RETRACTABIT core bit segment is composed of individual members having a matrix bonded to a lower end thereof, it is thought that the bond strength of the matrix to each member may be less than the bond strength of the matrix to the conventional one piece cylindrical core bit.

[0007] The RETRACTABIT core bit can be manufactured in one of two ways. The first involves providing a cylindrical blank, bonding the matrix to one end of the blank in accordance with the technique used for the manufacture of standard core bits and then cutting the blank with the bonded matrix into individual segments and machining the surfaces of the segments. For an NQ size bit this method can produce four or more individual segments per blank.

[0008] An alternate method is to manufacture the members that compose the segments individually and then bond the matrix to them in say groups of four or five. This group size is largely dependent upon the standard size moulds and jigs used for applying the matrix. However, this method involves the method of relatively complex jigs in order to hold the individual members.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a bit segment of alternate configuration which in use limits the variation of core gauge to an acceptable level. It is a further object of the present invention to provide a method of manufacturing the drill bit segments.

[0010] According to the present invention there is provided a segment for a core drill bit, the segment comprising at least:

[0011] an elongated member having an upper end, a lower end, a front side and an opposite second side; and

[0012] a matrix attached to said lower end and extending toward said upper end along the first and second sides of the member.

[0013] Preferably the lower end of the member is provided with a lip turned upwardly to extend in front of the first side of the member to define a recess for seating a lower edge of a drive sub and where in said matrix extends up said lip on the outside of said recess.

[0014] Preferably said matrix includes a first side on the first side of the member and an opposite second side on the second side of the member and where for a lower portion of the matrix the first and second sides of the matrix are substantially parallel to each other and for an upper portion of the matrix the first and second sides of the matrix converge toward the first and second sides respectively of the member.

[0015] Preferably the first side of the matrix converges so as to meet an upper edge of the lip.

[0016] Preferably the second side of the matrix converges toward the second side of the member at a first location above a trough of the recess.

[0017] Preferably the matrix includes gauging means on the second side for cutting an outer surface, said gauging means disposed between said trough and said first location.

[0018] Preferably the first side of the matrix commences to converge toward the first side of the member at a point above the lower end of the member.

[0019] Preferably the point at which the first side of the matrix commences to converge toward the member is below the trough of the recess.

[0020] According to the present invention there is also provided a method of manufacturing a bit segment for a core drill bit including the steps of:

[0021] forming a plurality of side by side members with mutually adjacent members joined by integrally formed webs, the members juxtaposed to form a cylinder like structure, each member having an upper end, a lower end, a first side and an opposite second side, with the cylinder like structure having a lower end defined by the lower ends of the members, and an upper end defined by the respective upper ends of the members;

[0022] forming a matrix at the lower end of the cylinder like structure;

[0023] configuring the matrix so that it extends across the lower end of the cylinder like structure and up the first and second sides of the members toward the upper ends of the members; and

[0024] fragmenting said cylinder like structure into separate segments each of which comprises a member with matrix attached at its lower end, the matrix extending toward the upper end of the member along the first and second sides of the member.

[0025] Preferably the method includes, for an NQ size core drill bit, forming said cylinder like structure with six side by side members.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

[0027]FIG. 1 is a side view of a core drill bit segment in accordance with an embodiment of this invention;

[0028]FIG. 2 is a bottom view of the segment shown in FIG. 1;

[0029]FIG. 3 is a perspective view of a blank used in the manufacture of the segment shown in FIG. 1;

[0030]FIG. 4 is a front view of the blank shown in FIG. 3;

[0031]FIG. 5 is a longitudinal section view of the blank shown in FIGS. 3 and 4;

[0032]FIG. 6 is a bottom view of the blank;

[0033]FIG. 7 is a top view of the blank;

[0034]FIG. 8 is a section view of a core drill bit segment loaded into a drive sub; and

[0035]FIG. 9 is an enlarged view of detail A of FIG. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036]FIGS. 1 and 2 depict a core drill bit segment 10 in accordance with an embodiment of the present invention. The segment 10 comprises an elongated member 12 having an upper end 14, a lower end 16, first side 18 and opposite second side 20. Attached to the lower end 16 is matrix 22. The matrix 22 is of conventional opposition and includes a combination of metallic powders and diamonds that are in effect fused to the lower end 16 by application of heat and pressure. As is most apparent from FIG. 1, the matrix 22, while depending from the lower end 16 also extends upwardly toward the upper end 14 along the first and second side 18, 20 of the member 12.

[0037] The lower end 16 of the member 12 is provided with a lip 24 that is turned upwardly to extend in front of the first side 18 to define a recess 26 for seating a lower edge of a drive sub 25 (shown in FIGS. 8 and 9). It will be noted that the matrix 22 extends along the lip 24 on the outside of the recess 26.

[0038] More particularly, the matrix 22 has a first side 28 on the first side 18 of the member 12, an opposite side 30 on the second side 20 of the member 12, and a bottom planar side 32 extending transversely to and joining at opposite edges the first and second sides 28 and 30.

[0039] For a lower portion of the matrix 22, the first and second sides 28, 30 are substantially parallel to each other. However, for an upper portion of the matrix, the surfaces 28 and 30 converge toward the first and second sides 18, 20 respectively of the member 12. The point of convergence is, in this embodiment, different for the opposite surfaces 28 and 30 of the matrix. The surface 28 commences to converge toward the side 18 at a point 34 that is located above the lower end 16 of the member but lower than trough 36 of the recess 26. The surface 28 converges so as to meet upper edge 38 of the lip 24.

[0040] Surface 30 commences to converge toward side 20 at a point 40. The point 40 is located above the trough 36 (and thus above point 34) and in approximate alignment with the upper edge 38 of lip 24.

[0041] Gauge cutting means such as diamonds or tungsten carbide pieces/buttons 41 are bonded to surface 30 in a region between the immediate vicinity of trough 36 and point 40. The gauge cutting means cut the gauge or outer diameter of the core sample.

[0042]FIGS. 8 and 9 depict a segment 10 loaded or coupled to a drive sub 25. The drive sub 25 is provided with a tapered region 27 in the vicinity of its lowest axial end 29. The taper 27 is configured so that the outer diameter of the drive sub 25 decreased in the direction toward its lower edge 29. When a segment 10 is loaded or coupled to the drive sub 25 the taper 27 seats in the recess 26. However as shown in FIG. 8, the recess 26 is configured so that it does not match the configuration of the taper 27. More specifically, the recess 26 is deliberately mismatched to the taper 27 in a manner so as to encourage pivoting of the segment 10 about the bottom of the trough 36 in a direction away from an axis of the drive sub 24 as indicated by arrow P. This is done by configuring the recess 26 so that a face of the recess 31 coterminous with side 18 of member 12 seats substantially flush against an inside surface of the taper 27 while an opposite surface 33 of the recess 26 slopes away from the taper 27 in the direction from trough 36 to the upper edge 38.

[0043] As a consequence of this mismatching of the recess 26 with the taper 27 if excess weight is applied any pivotal motion of the lower end of the member 12 and the matrix 22 will be about the trough 36 in a direction away from the central axis of the drive sub 25. Due to the location of the gauge stones 41 such motion results in the gauge stones 41 travelling along an arcuate path displacing them initially in a direction toward the longitudinal axis of drive sub 25 and then away from that axis. In terms of the gauge of the core cut this results in an initial minor reduction in the gauge of the core and a similar increase in the gauge. This variation in the gauge is in the order of 0.5 mm. It is found that such limited variation in the core gauge avoids the problems in the prior art of the core either being too small to be gripped by the core catcher, or alternately being too large to be received within the core tube.

[0044] The method of manufacturing segment 10 will now be described with reference to FIGS. 3-7.

[0045] The initial step in manufacturing the bit segment 10 is to form a cylinder like structure or blank 42. The blank 42 is composed of a plurality (in this instance six) side by side members 12 a-12 f (hereinafter referred to in general as members 12(i) where mutually adjacent members 12(i) are joined by integrally formed webs 44. The members 12(i) are of identical shape and orientation and are aligned so that their upper ends 14 and lower ends 16 lie in respective common spaced apart horizontal planes. The blank 42 has an upper end 46 defined by the upper ends 14 of the members 12(i) and a lower end 48 defined by the lower ends 16 of the members 12(i). The blank 42 could in theory be made by moulding, however it is preferred that the blank 42 be made by machining a cylindrical tube to define the individual members 12(i) and adjoining webs 44.

[0046] The next stage in the manufacture is to form the matrix 22 together with the gauge cutting means 41 at the lower end 48 of the blank 42. In this step, the matrix is configured so that it extends across the lower end 48 of the blank 42 and up the first and second sides 18, 20 respectively of each of the members 12 i.

[0047] This can be achieved by placing the blank 42 in a substantially conventional jig used for applying matrix to a standard core bit, depositing matrix material in particulate or powder form in the jig and then subjecting the jig with the blank and the matrix powder to the conventional cooking cycle. Once the matrix has been fused to the lower end 48 of the blank 42, the blank 42 is fragmented into individual segments 10. Typically this is achieved by cutting the individual members 12 a away from the adjoining webs 44.

[0048] This manufacturing technique enables the production of six segments 10 for an NQ sized core bit using one blank 42. As only four segments 10 are required for the RETRACTABIT core drill bit equivalent to an NQ size drill bit, this translates to production of one and a half drill core bits per cooking cycle. In comparison, the current method of manufacture at best produces four or five segments 10.

[0049] Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, with reference to the segment 10 illustrated in FIGS. 1-3, the specific configuration of sides 18 and 20 can be varied in accordance with the configuration of a surface of a drive sub or bit locking sleeve used for locking the segments 10 in a cutting position. Also, if desired a tang can be provided at the bottom end 16 of the member 12 to increase the bonding surface area for the matrix 22. Also, the shape and configuration of the webs 44 adjoining adjacent members 12(i) in the blank 42 can be made of any desired shape and configuration.

[0050] All such modifications and variations together with others that would be obvious to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims. 

1. A segment for a core drill bit, the segment comprising at least: an elongated member having an upper end, a lower end, a first side and an opposite second side, said lower end of the member provided with a lip turned upwardly to extend in front of the first side of the member to define a recess for seating a lower edge of a drive sub; and a matrix attached to said lower end and extending toward said upper end up said lip on an outside of said recess and along said second side of the member.
 2. A segment according to claim 1 wherein said matrix includes a first side on the first side of the member and an opposite second side on the second side of the member and where for a lower portion of the matrix the first and second sides of the matrix are substantially parallel to each other and for an upper portion of the matrix the first and second sides of the matrix converge toward the first and second sides respectively of the member.
 3. The segment according to claim 1 or 2 wherein the first side of the matrix converges so as to meet an upper edge of the lip.
 4. The segment according to any one of claims 1 to 3 wherein the second side of the matrix converges toward the second side of the member at a first location above a trough of the recess.
 5. The segment according to any one of claims 1 to 4 wherein the matrix includes gauging means on the second side for cutting an outer surface, said gauging means disposed between said trough and said first location.
 6. The segment according to any one of claims 1 to 5 wherein the first side of the matrix commences to converge toward the first side of the member at a point above the lower end of the member.
 7. The segment according to any one of claims 1 to 6 wherein the point at which the first side of the matrix commences to converge toward the member is below the trough of the recess.
 8. A method of manufacturing a bit segment for a core drill bit including the steps of: forming a plurality of side by side members with mutually adjacent members joined by integrally formed webs, the members juxtaposed to form a cylinder like structure, each member having an upper end, a lower end, a first side and an opposite second side, with the cylinder like structure having a lower end defined by the lower ends of the members, and an upper end defined by the respective upper ends of the members; forming a matrix at the lower end of the cylinder like structure; configuring the matrix so that it extends across the lower end of the cylinder like structure and up the first and second sides of the members toward the upper ends of the members; and fragmenting said cylinder like structure into separate segments each of which comprises a member with matrix attached at its lower end, the matrix extending toward the upper end of the member along the first and second sides of the member.
 9. A method according to claim 8 further included the step of, for an NQ size core drill bit, forming said cylinder like structure with six side by side members.
 10. A method according to claim 8 or 9 wherein said step of forming a plurality of side by side members includes machining a tubular blank to form said members. 